IMO at around this age, boys especially, tend to develop obsessions and become fanatical over certain things. DS has done the computer thing. It is curretnly football.
It is so frustrating when he has such a one track mind and half heartedly attempts everything he does other than his latest obsession
I have found the only way to deal with this is to really crack down. Use the obsession to your advantage. We have the 3 golden rules here. Written up and on the fridge. We agreed them with DS and one of them relates to what we refer to as Smacked Backside Face which occured when pc time was up, asked to do anything to help, get dressed, endless list of just daily stuff that he would manage to have a strop about. (huffing, puffing, lolling on sofa) This Is Not Allowed.
If he breaks the No Smacked Backside Face rule, then he loses PC/PS2 for a day.
It took a couple of goes for him to realise that we really did mean it but there has been a much better response from him to the time limits playing on computer stuff, his attitude to siblings, participating in family life.
This may seem harsh but I swear that all other approaches just hadn't worked.
The list is still on the fridge as a reminder and if he starts playing up i usually point him in the direction of the kitchen to take a look and he snaps out of it.
Sorry so longwinded. You are not alone in feeling like this about your DS.